The disclosure of Japanese Patent Application No. 2001-106116 filed on Apr. 4, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a voltage conversion apparatus that performs voltage conversion between charging/discharging devices, such as batteries and capacitors. More particularly, the invention is concerned with a voltage conversion apparatus adapted to change a value or level of a voltage of a charging/discharging device, such as a battery or a capacitor, and apply the resulting voltage having a different value to another charging/discharging device.
2. Description of Related Art
To meet with a demand for environmental protection in recent years, there have been developed vehicles using regeneration or restoration control for improving the fuel economy by converting the kinetic energy of the vehicle into the electric energy during braking (i.e., by performing regenerative braking). In the regeneration control, regenerated energy obtained through regenerative braking is initially received by a capacitor, and a value of a voltage of the capacitor is then changed so that the resulting electric power is supplied to a battery installed on the vehicle.
As one example of the voltage conversion apparatus using the regeneration control as described above, there is known a step-up/step-down converter that performs charging and discharging of two condensers, as disclosed in Laid-open Publication No. 6-66204 of Utility Model Application. The step-up/step-down converter is constructed such that a reactor is connected to one of the condensers, and a switching device and a diode are connected between the output of the reactor and the earth (ground). In addition, a switching device and a diode are connected between the output of the reactor and the other condenser. In a step-up operation, the switching device connected between the output of the reactor and the other condenser is kept in the ON state, and the switching device connected between the output of the reactor and the earth is switched on and off, so that a high voltage is applied to the other condenser. In a step-down operation, on the other hand, the switching device connected between the output of the reactor and the other condenser is switched on and off, and the switching device connected between the output of the reactor and the earth is kept in the ON state, so that a low voltage is applied to the other condenser.
However, the step-up/step-down converter as described above has a problem of discontinuity in its operation when the voltage conversion ratio is in the vicinity of 1.
For example, the ratio of output voltage to input voltage in a step-up operation of the step-up/step-down converter is equal to 1/(1xe2x88x92xcex3), where xcex3 represents switching duty ratio (TON/(TON+TOFF)) of the switching device. On the other hand, the ratio of output voltage to input voltage in a step-down operation of the converter is equal to xcex3. FIG. 5 shows the relationship between the duty ratio xcex3 of the switching device and the ratio of the output voltage to the input voltage in step-up and step-down operations of the converter. As is understood from FIG. 5, the duty ratio xcex3 of the switching device needs to be changed when the step-up/step-down converter shifts from a step-down operation to a step-up operation, for example, resulting in discontinuity in the operation of the switching device.
It is therefore one object of the invention to provide a voltage conversion apparatus that permits smooth shifting or switching between step-up operations and step-down operations.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention, a voltage conversion apparatus which is connected between a first charging/discharging device and a second charging/discharging device and which performs voltage conversion between the first charging/discharging device and the second charging/discharging device. The voltage conversion apparatus includes: (a) a first switching device having a first terminal and a second terminal, the first terminal being connected to the first charging/discharging device, (b) a second switching device connected between the second terminal of the first switching device and the earth, (c) a third switching device having a third terminal and a fourth terminal, the third terminal being connected to the second charging/discharging device, (d) a fourth switching device connected between the fourth terminal of the third switching device and the earth, (e) a coil provided between the second terminal of the first switching device and the fourth terminal of the third switching device, and (f) a controller that controls operations of the first switching device, the second switching device, the third switching device and the fourth switching device, such that the first switching device and the fourth switching device are switched on and off in a first phase, and the second switching device and the third switching device are switched on and off in a second phase that is reverse to the first phase of switching of the first switching device and the fourth switching device.
In one embodiment of the invention, the first charging/discharging device is charged by use of braking energy of a vehicle.
In the voltage conversion apparatus constructed according to this aspect of the invention, the operations of the first through fourth switching devices are controlled such that the first switching device and the fourth switching device are switched on and off in the same phase, and the second switching device and the third switching device are switched on and off in the same phase that is reverse to the phase of switching of the first and fourth switching devices. Thus, the four switching devices provide a step-up/step-down chopper in which a step-down chopper and a step-up chopper are connected in series. The thus constructed voltage conversion apparatus permits continuous switching from a step-up operation to a step-down operation, or vice versa, by continuously varying the duty ratio of switching of the switching devices. This arrangement makes it possible to avoid noise and false operations due to the noise, upon switching from a step-down operation to a step-up operation or vice versa.